Purpose: To determine the reliability of early force production (50, 100, 150, 200, and 250 ms) relative to peak force (PF) during an isometric mid-thigh pull and to assess the relationships between these variables. Methods: Male collegiate athletes (N = 29; age 21.1 [2.9] y, height 1.71 [0.07] m, body mass 71.3 [13.6] kg) performed isometric mid-thigh pulls during 2 separate testing sessions. Net PF and net force produced at each epoch were calculated. Within- and between-session reliabilities were determined using intraclass correlation coefficients and coefficient of variation percentages. In addition, Pearson correlation coefficients and coefficient of determination were calculated to examine the relationships between PF and time-specific force production. Results: Net PF and time-specific force demonstrated very high to almost perfect reliability both within and between sessions (intraclass correlation coefficients .82–.97; coefficient of variation percentages 0.35%–1.23%). Similarly, time-specific force expressed as a percentage of PF demonstrated very high to almost perfect reliability both within and between sessions (intraclass correlation coefficients .76–.86; coefficient of variation percentages 0.32%–2.51%). Strong to nearly perfect relationships (r = .615–.881) exist between net PF and time-specific net force, with relationships improving over longer epochs. Conclusion: Based on the smallest detectable difference, a change in force at 50 milliseconds expressed relative to PF > 10% and early force production (100, 150, 200, and 250 ms) expressed relative to PF of >2% should be considered meaningful. Expressing early force production as a percentage of PF is reliable and may provide greater insight into the adaptations to the previous training phase than PF alone.
Paul Comfort, Thomas Dos’Santos, Paul A. Jones, John J. McMahon, Timothy J. Suchomel, Caleb Bazyler and Michael H. Stone
Daniel Bok and Igor Jukić
Purpose: To report creatine kinase ([CK]) responses during a soccer World Cup preparatory and first-leg period and to determine the influence of aerobic fitness on postmatch [CK] responses. Methods: Eleven national-team players were analyzed in this study. A lactate threshold test was performed during the first 3 d, whereas fingertip blood was drawn most mornings (21 out of 30 d) for [CK] measurements. One-way repeated-measures analysis of variance was used for determining the effect of time on [CK] measurements, whereas Pearson correlation coefficient was used for assessing associations between the changes in [CK] and velocities associated with blood lactate concentrations of 2 (v2) and 4 mmol·L−1 (v4). Results: Peak [CK] concentrations were consistently reached on the first day after the match with values of 474 (261), 520 (419), and 460 (126) U·L−1 but with no significant differences between them. [CK] concentrations returned to prematch values (331  U·L−1) on the second day after the match. The change in [CK] concentration between prematch and postmatch day was largely correlated (r = .614, P = .044) with v2. Conclusions: Top-level soccer players display low levels of muscle damage during official tournaments, and they recover before the next match. Postmatch muscle damage is greater in players with higher aerobic endurance because this fitness quality enables them to execute high-intensity activities known to be a major contributor to muscle damage.
Pedro L. Valenzuela, Guillermo Sánchez-Martínez, Elaia Torrontegi, Javier Vázquez-Carrión, Manuela González, Zigor Montalvo and Grégoire P. Millet
Purpose: Repeated-sprint training (RS) is commonly conducted in normoxia, but its completion with localized (blood-flow restriction [BFR]) or systemic hypoxia has been proven effective for performance enhancement. Yet, few studies have applied these types of RS sessions in racket sports. The authors aimed to determine the acute responses to these types of training in elite badminton players. Methods: Eight male elite badminton players participated in this randomized crossover study. They performed 3 on-court RS sessions, each consisting of 3 sets of 10 repetitions of 10-s badminton-specific movements in normoxia (RSN), systemic normobaric hypoxia (RSH, FiO2 = 14%), or with BFR (RS-BFR, 40% arterial occlusion pressure). Performance, perceptual (ie, rating of perceived exertion), and physiological (ie, pulse saturation, muscle oxygenation, blood lactate, creatine kinase, heart-rate variability) responses were measured after each set and up to 48 h postsession. Results: RS-BFR induced a greater performance impairment (lower distance and accelerations) and a higher local perceived exertion in the legs than RSN and RSH (P < .05), whereas greater overall fatigue was reported with RSH (P < .05). RSH induced a lower saturation (P < .001), but no differences were observed in muscle oxygenation between conditions. No differences in creatine kinase or heart-rate variability were observed at any time point (from baseline up to 48 h after the session). Conclusions: RS-BFR—and, to a lower extent, RSH—resulted in impaired performance and a higher perceived strain than RSN. However, these 2 hypoxic methods do not seem to induce a long-lasting (post 24–48 h) physiological stress in elite badminton players.
Ida A. Heikura, Marc Quod, Nicki Strobel, Roger Palfreeman, Rita Civil and Louise M. Burke
Purpose: To assess energy and carbohydrate (CHO) availability and changes in blood hormones in 6 professional male cyclists over multiple single-day races. Methods: The authors collected weighed-food records, power-meter data, and morning body mass measurements across 8 d. CHO intakes were compared with contemporary guidelines. Energy availability (EA) was calculated as energy intake minus exercise energy expenditure, relative to fat-free mass (FFM). Skinfold thickness and blood metabolic and reproductive hormones were measured prestudy and poststudy. Statistical significance was defined as P ≤ .05. Results: Body mass (P = .11) or skinfold thickness (P = .75) did not change across time, despite alternate-day low EA (14  vs 57  kcal·kg−1 FFM·d−1, race vs rest days, respectively; P < .001). Cyclists with extremely low EA on race days (<10 kcal·kg−1 FFM·d−1; n = 2) experienced a trend toward decreased testosterone (−14%) and insulin-like growth factor 1 (−25%), despite being high EA (>46 kcal·kg−1 FFM·d−1) on days between. CHO intakes were significantly higher on race versus rest days (10.7 [1.3] vs 6.4 [0.8] g·kg−1·d−1, respectively; P < .001). The cyclists reached contemporary prerace fueling targets (3.4 [0.7] g·kg−1·3 h−1 CHO; P = .24), while the execution of CHO guidelines during race (51  g·h−1; P = .048) and within acute (1.6 [0.5] g·kg−1·3 h−1; P = .002) and prolonged (7.4 [1.0] g·kg−1·24 h−1; P = .002) postrace recovery was poor. Conclusions: The authors are the first to report the day-by-day periodization of energy and CHO in a small sample of professional cyclists. They also examined the logistics of conducting a field study under stressful conditions in which major cooperation from the subjects and team management is needed. Their commentary around these challenges and possible solutions is a major novelty of the article.
Owen Jeffries, Mark Waldron, Stephen D. Patterson and Brook Galna
Purpose: Regulation of power output during cycling encompasses the integration of internal and external demands to maximize performance. However, relatively little is known about variation in power output in response to the external demands of outdoor cycling. The authors compared the mean power output and the magnitude of power-output variability and structure during a 20-min time trial performed indoors and outdoors. Methods: Twenty male competitive cyclists (
Oliver Gonzalo-Skok, Alejandro Moreno-Azze, José Luis Arjol-Serrano, Julio Tous-Fajardo and Chris Bishop
Purpose: To compare the effects of performing different unilateral strength training interventions on unilateral and bilateral jumping performance and their related asymmetries in young soccer players. Methods: Forty-five young (U-17) male soccer players were randomly assigned to 3 eccentric overload training programs. The first group executed the same volume with both legs starting with the weaker leg (SVW, n = 15); the second group carried out double volume with the weaker leg and also starting with the weaker leg (DVW, n = 15); and the third group performed the same volume with both legs starting with the stronger leg (SVS, n = 15). Jumping-performance assessment included a single-leg horizontal jump test, a triple single-leg horizontal jump test, a bilateral countermovement jump (CMJ) test, and a unilateral CMJ test. Asymmetries were also analyzed in the unilateral jumping tests. Results: CMJ was improved (effect size [ES]: 0.27–0.48) and CMJ asymmetry was possibly reduced (ES: 0.08–0.24) in all groups. Substantial improvements were found in triple hop (ES: 0.52–0.71) in SVW and DVW, and triple-hop asymmetry was substantially decreased (ES: 0.88) in DVW. Between-groups analysis showed a substantially better performance in triple hop and horizontal hop with right leg in SVW and DVW compared with SVS. Conclusions: Unilateral strength training programs were shown to substantially improve bilateral jumping performance, while unilateral jumping was substantially enhanced in the groups that started the training session with the weaker leg. Finally, between-limbs asymmetries in the triple hop were mainly reduced through performing double volume with the weaker leg.
Chelsie E. Winchcombe, Martyn J. Binnie, Matthew M. Doyle, Cruz Hogan and Peter Peeling
Purpose: To determine the reliability and validity of a power-prescribed on-water (OW) graded exercise test (GXT) for flat-water sprint kayak athletes. Methods: Nine well-trained sprint kayak athletes performed 3 GXTs in a repeated-measures design. The initial GXT was performed on a stationary kayak ergometer in the laboratory (LAB). The subsequent 2 GXTs were performed OW (OW1 and OW2) in an individual kayak. Power output (PWR), stroke rate, blood lactate, heart rate, oxygen consumption, and rating of perceived exertion were measured throughout each test. Results: Both PWR and oxygen consumption showed excellent test–retest reliability between OW1 and OW2 for all 7 stages (intraclass correlation coefficient > .90). The mean results from the 2 OW GXTs (OWAVE) were then compared with LAB, and no differences in oxygen consumption across stages were evident (P ≥ .159). PWR was higher for OWAVE than for LAB in all stages (P ≤ .021) except stage 7 (P = .070). Conversely, stroke rate was lower for OWAVE than for LAB in all stages (P < .010) except stage 2 (P = .120). Conclusions: The OW GXT appears to be a reliable test in well-trained sprint kayak athletes. Given the differences in PWR and stroke rate between the LAB and OW tests, an OW GXT may provide more specific outcomes for OW training.
Øyvind Skattebo, Thomas Losnegard and Hans Kristian Stadheim
Purpose: Long-distance cross-country skiers specialize to compete in races >50 km predominantly using double poling (DP). This emphasizes the need for highly developed upper-body endurance capacities and an efficient DP technique. The aim of this study was to investigate potential effects of specialization by comparing physiological capacities and kinematics in DP between long-distance skiers and skiers competing using both techniques (skating/classic) in several competition formats (“all-round skiers”). Methods: Seven male long-distance (32  y, 183  cm, 76  kg) and 6 all-round (25  y, 181  cm, 75  kg) skiers at high international levels conducted submaximal workloads and an incremental test to exhaustion for determination of peak oxygen uptake (VO2peak) and time to exhaustion (TTE) in DP and running. Results: In DP and running maximal tests, TTE showed no difference between groups. However, long-distance skiers had 5–6% lower VO2peak in running (81  vs 85  mL·kg−1·min−1; P = .07) and DP (73  vs 78  mL·kg−1·min−1; P < .01) than all-round skiers. In DP, long-distance skiers displayed lower submaximal O2 cost than all-round skiers (3.8 ± 3.6%; P < .05) without any major differences in cycle times or cyclic patterns of joint angles and center of mass. Lactate concentration over a wide range of speeds (45–85% of VO2peak) did not differ between groups, even though each workload corresponded to a slightly higher percentage of VO2peak for long-distance skiers (effect size: 0.30–0.68). Conclusions: The long-distance skiers displayed lower VO2peak but compensated with lower O2 cost to perform equally with the all-round skiers on a short TTE test in DP. Furthermore, similar submaximal lactate concentration and reduced O2 cost could be beneficial in sustaining high skiing speeds in long-duration competitions.
Layne Case and Joonkoo Yun
Despite the rising interest in intervention for children with autism spectrum disorder, the extent to which interventions are effective on gross motor outcomes is currently unknown. The purpose of this study was to analyze the effect of different intervention approaches on gross motor outcomes among children with autism spectrum disorder using meta-analysis. A total of 18 studies met the inclusion criteria for quantitative analysis. Pre- and posttest means and SDs were extracted to calculate effect sizes. Potential moderator variables were chosen based on important intervention characteristics. The results suggest that interventions have a large effect on gross motor outcomes among children with autism spectrum disorder (δ = 0.99, SE = 0.19, p < .001, 95% confidence interval [0.62, 1.36]). The interventions that were 16 total hours or longer had a significantly larger effect than those less than 16 hr. In addition, the interventions in experimental settings had significantly larger effects than the interventions in practical settings. Future interventions should consider intensity, including not only the duration of the intervention but also the intensity in which specific intervention goals are targeted.
Iva Obrusnikova, Haley M. Novak and Albert R. Cavalier
Adults with intellectual disability have significantly lower musculoskeletal fitness than their peers without a disability. Appropriate instructional strategies are needed to facilitate their acquisition and maintenance of musculoskeletal fitness. In this multiple-baseline across-participants single-subject study, the authors evaluated the effects of a multicomponent package that included a video-enhanced system of least-to-most prompts on the acquisition of 5 muscle-strengthening exercises in 3 women with mild intellectual disability, age 24–37 yr. Results show substantive gains in correct and independent performance of steps in the 5 exercises during the treatment condition. The improved performance was maintained 2 wk after the last treatment session and in a large YMCA gym. The study suggests that use of the video-enhanced system of least-to-most prompts can lead to improved acquisition and maintenance of muscle-strengthening exercises by adults with mild intellectual disability.